A subject rarely found in circuit design textbooks is the matter of nonlinear junction capacitance, especially reverse-bias junction capacitance, also called depletion capacitance. When it is discussed, it’s usually with regard to fast switching circuits, and even then, it’s normally treated as linear.
Yet in many situations, junction capacitance will be found to be the main cause of distortion in otherwise highly linear analog circuits. This article is principally concerned with two instances of this phenomenon, often encountered simultaneously: input protection circuits and common-mode distortion in op amps.